Same problem here. Those colours are not only ugly, but also they tend to slow down the output significantly. The way I fix this is:
Changing The Terminal Colour
There’s no way to change the colour from the terminal in geany and some others like xterm, kitty, cool-retro-term etc.
But if you use gnome-terminal, xfce-terminal, tilix, terminology, etc. you can go to the settings and change the colour for deep blue and red:
Disable IRB Colour
The other idea is to disable colour with
--nocolorize or by writing
IRB.conf[:USE_COLORIZE] = false to the ~/.irbrc file.
I agree that IRB should use a different colour, like some light blue (
\e[38;2;100;150;255m but unchangeable), and red colours that’s readable in both black and white terminal with some transparency as well.